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libbb: use sendfile() to copy data between file descriptors

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Busybox already uses sendfile in httpd. This patch proposes to use it
globally to copy data between file descriptors.

It speeds up the copying on slow systems a lot - below are the times needed
to copy a 450Mb file with and without this option enabled on a BeagleBone
Black:

sendfile:
user    0m0.000s
sys     0m8.170s

read/write 4k:
user    0m0.470s
sys     0m16.300s

function                                             old     new   delta
bb_full_fd_action                                    394     474     +80

Signed-off-by: Bartosz Golaszewski <bartekgola@gmail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Bartosz Golaszewski
2014-11-27 13:20:24 +01:00
committed by Denys Vlasenko
parent ee41094b80
commit 8d75d794ea
4 changed files with 71 additions and 42 deletions
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12
Config.in
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@@ -264,6 +264,18 @@ config PAM
Use PAM in some busybox applets (currently login and httpd) instead
of direct access to password database.
config FEATURE_USE_SENDFILE
bool "Use sendfile system call"
default y
help
When enabled, busybox will use the kernel sendfile() function
instead of read/write loops to copy data between file descriptors
(for example, cp command does this a lot).
If sendfile() doesn't work, copying code falls back to read/write
loop. sendfile() was originally implemented for faster I/O
from files to sockets, but since Linux 2.6.33 it was extended
to work for many more file types.
config LONG_OPTS
bool "Support for --long-options"
default y